Fundamentals Of

Electric circuits

INDEX Introduction Principal Elements Voltage And Kirchhoff’s Voltage Law (KVL) Current And Kirchhoff’s Current Law (KCL) Types Of Circuits Resistance And Ohm’s Law Voltage Divider Rule (VDR) Current Divider Rule (CDR) Superposition Theorem

INTRODUCTION “An Electric Circuit is an

interconnection of electrical elements.” There are many elements used in an circuit:

1. Sources2. Branch & Node3. Loop & Mesh4. Resistor 5. Inductor6. Capacitor7. Switch8. Wire

DEPENDENT SOURCE:1. Dependent Sources are whose input

(current or voltage) is a function of some other voltage or current in a circuit.

2. The symbols typically used to represent dependent sources are in the shape of a diamond.

INDEPENDENT SOURCE:

1. Independent Sources have the capability of generating a prescribed voltage or current independent of any other element within the circuit.

2. These sources may output constant voltage/current that varies with time.

BRANCH & NODE Branch is any portion

of circuit with two terminals connected with it. It may consist of one or more circuit elements.

Node is the point of connection between two or more branches. A node usually indicated by a dot in a circuit.

LOOP & MESH Loop is any closed

path through the circuit in which no node is encountered more than once.

Mesh is a loop that does not contain any other loops.

VOLTAGE & KVL Voltage is the total work per unit charge

associated with the motion of charge between two points. The unit of voltage is Volt (v).

Kirchhoff’s Voltage Law (KVL) states that, “The net voltage around a closed circuit is zero.” This means, algebraic sum of the potential rises and drops around a closed loop or path is zero.

CURRENT & KCL Current is defined as the time rate of

change of charge passing through a predetermined area. The unit of electric current is called Ampere (A).

Kirchhoff’s Current Law (KCL) states that, “The sum of the currents at a node must equal to zero.” That means, the algebraic sum of current entering and leaving a node is equal to zero.

or

RESISTANCE & OHM’S LAW An ideal Resistor is a device that

exhibits linear resistance properties according to Ohm’s Law, which states that, “The voltage across a resistance is directly proportional to the current flowing through it.”

V = IR where R is resistance, whose unit is

measured in Ohm.

TYPES OF CIRCUIT Open Circuit: A

circuit element whose resistance approaches infinity.

Short Circuit: A circuit element whose resistance approaches zero.

SERIES CIRCUIT Two or more circuit elements are said

to be in Series if the current from one element exclusively flows in to the next elements. All series elements have the same current and there is only one common point between two elements.

PARALLEL CIRCUIT Two or more circuit elements are said

to be in Parallel if the elements share the same terminals. All parallel elements have the same voltage and there is more than one common point between two elements.

VOLTAGE DIVIDER RULE VDR is useful in determining the voltage

drop across a resistance within a series circuit.

Where, VX = the voltage drop across the measured

resistor, RX = the voltage drop across the measured

resistor, REQ = the circuit total resistance, VS = the circuit applied voltage

CURRENT DIVIDER RULE (CDR) CDR is useful in determining the current

flow through one branch of a parallel circuit.

where, IX = the current flow through any parallel

branches, RX = the resistance of the branch through

the current is to be determined, REQ = the total resistance of the parallel

branch,IS = the circuit applied current